A 16-yr-old girl was hospitalized because of amenorrhea and virilism, and was diagnosed with an adrenal tumor on the right side. Her serum androgen levels were markedly elevated, and severe hypocholesterolemia (total cholesterol, 0.59 mmol/L) was observed. After resection of the tumor, her serum cholesterol level dramatically rose to normal, suggesting a role of this tumor in her marked hypocholesterolemia. To investigate the mechanism of hypocholesterolemia in this case, we examined the effects of dehydroepiandrosterone and dehydroepiandrosterone sulfate on the low density lipoprotein (LDL) receptor activity of fibroblasts. These hormones did not have any effect on LDL receptor activity. Northern blot analysis demonstrated that the LDL receptor messenger ribonucleic acid level of this tumor tissue was increased about 8-fold compared with that of normal adrenal cortex. The LDL receptor activity of the cultured cells established from this tumor was 2-fold higher than that of Hep G2 cells. Furthermore, the LDL receptor activity could not be down-regulated by an excessive dose of 25-hydroxycholesterol. These results suggest that increased LDL receptor activity and unrestricted uptake of LDL by the adrenal tumor may have caused the marked hypocholesterolemia in this patient.